System for insulating an induction vacuum furnace and method of making same

ABSTRACT

A system and method for insulating an induction vacuum furnace is disclosed. An induction furnace for heating a workpiece includes a chamber, an insulation cylinder positioned within the chamber, and an induction coil positioned to surround at least a portion of the insulation cylinder. A susceptor is positioned within the insulation cylinder and inductively heated by the induction coil when a current is provided to the induction coil. An insulating jacket assembly including one of a carbide material and a refractory metal is positioned in a space between the insulating cylinder and the susceptor.

CROSS-REFERENCE TO RELATED APPLICATION

This is a national stage application under 35 U.S.C. §371(c) ofprior-filed, co-pending, PCT application serial numberPCT/US2013/038796, filed on Apr. 30, 2013, which claims priority to U.S.Provisional Application No. 61/694,869, filed Aug. 30, 2012, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to induction furnaces forheating a workpiece in an inert atmosphere or vacuum and, moreparticularly, to a system for providing an insulation package for aninduction furnace having improved insulation properties at temperaturesabove 1200 degrees Celsius.

Conventional induction furnaces include an induction heating system anda chamber that contains a susceptor that is susceptible to inductionheating, with the chamber enclosing an inert atmosphere or vacuumtherein. An electromagnetic coil sits outside the susceptor and receiveshigh frequency alternating current from a power supply. The resultingalternating electromagnetic field heats the susceptor rapidly. Theworkpiece to be heated is placed in proximity to and generally withinthe susceptor so that when the susceptor is inductively heated by theinduction heating system, the heat is transferred to the workpiecethrough radiation and/or conduction and convection. After a desiredheating and processing of the workpiece is completed, the workpiece isthen subsequently cooled in order to complete the heating/cooling cycle.

Induction heating can be used to bond, harden or soften metals or otherconductive materials in a wide variety of manufacturing processes. Theintended outcome of the induction heating process (e.g., bonding orhardening), the furnace efficiency and cycle time, as well as the size,geometry, and material properties of the workpiece are all factors thatmay be taken into account in a design of an induction furnace.

Prior art induction furnaces typically operate at temperatures at orbelow 1200 degrees Celsius. For certain manufacturing processes andworkpiece materials, however, it would be desirable to operate theinduction furnace at temperatures above 1200 degrees Celsius. Prior artinduction furnaces experience a number of negative effects whenoperating at temperatures above 1200 degrees Celsius. For example, theoperating efficiency of the furnace and the temperature uniformitywithin the furnace is negatively affected. Further, dielectric breakdowntends to occur around the induction coils of the furnace at furnaceoperating temperatures above 1200 degrees Celsius.

It would therefore be desirable to design an induction furnace capableof operating at temperatures above 1200 degrees Celsius, whilemaintaining efficient and uniform heating and preventing dielectricbreakdown around the induction coils.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention overcome the aforementioned drawbacks byproviding a system and method for insulating an induction vacuumfurnace.

In accordance with one aspect of the invention, an induction furnace forheating a workpiece includes a chamber, an insulation cylinderpositioned within the chamber, and an induction coil positioned tosurround at least a portion of the insulation cylinder. A susceptor ispositioned within the insulation cylinder and inductively heated by theinduction coil when a current is provided to the induction coil. Aninsulating jacket assembly including one of a carbide material and arefractory metal is positioned in a space between the insulatingcylinder and the susceptor.

In accordance with another aspect of the invention, an induction furnaceincludes a chamber having a susceptor positioned therein. An interiorvolume of the susceptor defines a zone within the chamber for heating aworkpiece. The induction furnace also includes an insulation packagehaving a fused quartz cylinder positioned around the susceptor and agraphite jacket positioned between the fused quartz cylinder and thesusceptor. A coil surrounds the insulation package and is configured toinductively heat the interior volume of the susceptor when a current isprovided to the induction coil.

In accordance with yet another aspect of the invention, a method ofmaking an induction furnace includes providing a vacuum chamber,coupling an insulation cylinder within the vacuum chamber, and couplingan induction coil to surround at least a portion of the insulationcylinder. The method also includes coupling a susceptor within theinsulation cylinder and encapsulating the susceptor with an insulatingjacket, wherein the insulating jacket comprises one of a carbidematerial and a refractory metal.

These and other advantages and features will be more readily understoodfrom the following detailed description of embodiments of the inventionthat is provided in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a block schematic diagram of an induction furnace according toan embodiment of the invention.

FIG. 2 is an additional diagram of the induction furnace of FIG. 1 wherea workpiece is in a lowered position.

FIG. 3 is a block schematic diagram of an induction furnace according toanother embodiment of the invention.

FIG. 4 is an additional diagram of the induction furnace of FIG. 3 wherea workpiece is in a lowered position.

FIG. 5 is a flowchart illustrating a technique for heating and cooling aworkpiece using an induction furnace according to an embodiment of theinvention.

FIG. 6 is a block schematic diagram of an induction furnace according toan alternative embodiment of the invention.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, the major components of an induction furnace100 are shown. Induction furnace 100 includes an induction heatingsystem 102 inside a chamber 104. Induction heating system 102 includesan insulation package 106 comprising an insulation cylinder 108 and aninsulating jacket assembly 110. Insulation cylinder 108 includes a sidewall 112, a first cover 114 for sealing one end of cylinder 108, and asecond cover 116 for sealing the second end of cylinder 108. Inductionheating system 102 includes a coil 118 and a power supply (not shown)that provides an alternating current that flows through coil 118 duringa heating cycle. Coil 118 is wound to form a helical shape withinchamber 104 about insulation cylinder 108 as shown in FIG. 1.

Contained within insulation cylinder 108 is a susceptor 120 that issusceptible to induction heating. That is, when an alternating currentflows through coil 118, an alternating magnetic field is generated thatinduces eddy currents and other effects in susceptor 120 that cause thesusceptor 120 to heat. The thermal energy that radiates from susceptor120 is used to heat a workpiece 122. Susceptor 120 is shown as beingcylindrical, but other shapes can be used. Susceptor 120 is made of anymaterial susceptible to induction heating, such as, for example,graphite, molybdenum, steel, and tungsten. Susceptor 120 is arrangedwithin insulation cylinder 108 in chamber 104. Insulation cylinder 108is made from an insulative material that is not susceptible to inductionheating such as, for example, fused quartz.

Susceptor 120 includes a side wall 124, a first cover 126 for sealingone end, and a second cover 128 for sealing the other end. A tray 130for supporting workpiece 122 to be heated is connected to second cover128 of susceptor 120. Although susceptor 120 is shown as having closedends, this need not be the case. For example, the susceptor 120 can bein the form of a tube that is open at both ends or, for example, it cancomprise one or more susceptor sheets. First cover 114 of cylinder 108is coupled to chamber 104 via one or more posts 132, which in anembodiment, is constructed of a ceramic material. First cover 126 ofsusceptor 120 is coupled to first cover 114 via one or more additionalposts 134.

Insulating jacket assembly 110 includes a plurality of insulating sheets136 arranged in layers to cover the exterior surfaces of susceptor 120.As shown in FIG. 1, insulating sheets 136 are contained in the spacebetween insulation cylinder 108 and susceptor 120 to prevent any loosematerial of insulating sheets 136 from contaminating the rest of thevacuum chamber or in the components being processed in induction furnace100. In particular, a first portion 138 of insulating sheets 136 ispositioned between outer surface 140 of side wall 124 of susceptor 120and an inner surface 142 of side wall 112 of insulation cylinder 108. Asecond portion 144 of insulating sheets 136 are positioned between a topsurface 146 of first cover 126 of susceptor 120 and an upper, insidesurface 148 of insulation cylinder 108. A third portion 150 ofinsulating sheets 136 is positioned between a bottom surface 152 ofsecond cover 128 and a lower, inside surface 154 of insulation cylinder108.

Each layer of the insulating sheets 136 may be, for example,approximately ⅛ inch thick, and is woven at a frequency such that thematerial is transparent to induction. In one exemplary embodiment, thefirst portion 138 of insulating sheets 136 includes three (3) individuallayers wrapped around susceptor 120, the second portion 144 ofinsulating sheets 136 includes four (4) individual layers sized toapproximately match the geometry of the first cover 126 of susceptor120, and third portion 150 of insulating sheets 136 includes ten (10)individual layers sized to approximately match the geometry of thesecond cover 128 of susceptor 120. However, one skilled in the art willrecognize that the number of layers of insulating sheets 136 as well asthe geometry and thickness of each layer may be varied based on desiredinsulating characteristics.

In one embodiment, insulation package 106 further includes an upperinsulating plate 156 positioned atop the second portion 144 ofinsulating sheets 136 and a lower insulating plate 158 positioned belowthe third portion 150 of insulating sheets 136 to further contain secondand third portions 144, 150 of insulating sheets 136. Upper and lowerinsulating plates 156, 158 retain insulating sheets 136 againstsusceptor 120 and provide additional insulation for susceptor 120. In anexemplary embodiment, upper insulating plate 156 and lower insulatingplate 158 are constructed of graphite.

Insulating sheets 136, which comprise carbides or refractory metals,insulate the outside of susceptor 120 and mitigate radiative heat loss.In an exemplary embodiment, insulating sheets 136 are layers of graphitefelt or wool. The graphite felt has a bulk density of approximately 0.10g/cm³, a carbon content greater than approximately 99.5 percent, an ashcontent of approximately 0.05 percent, a thermal conductivity at 1500degrees Celsius of approximately 0.08 W/mk, and a maximum processtemperature of approximately 2400 degrees Celsius. While graphitematerials are inherently susceptible to inductive heating, theconfiguration and arrangement of insulating sheets 136 within inductionfurnace 100 relative to the other elements of the insulating package,including insulation cylinder 108, minimizes the susceptibility ofinsulating sheets 136 to significant induction heating. Heat generatedby induction heating system 102 is used to heat susceptor 120 ratherthan being lost on heating insulating sheets 136. As such, susceptor 120is idealized for heating. Further, insulating sheets 136 are arranged soas to not heat each other and to not heat coil 118 at the elevatedoperating temperatures within the heating zone 164 of susceptor 120.

The graphite felt has a number of benefits over a traditional insulationpackage. For example, graphite felt has reduced susceptibility tocontamination, has no issue with thermal shock, and functions well invacuum. Ceramics, on the other hand, are brittle and prone to fracturein the high temperature environment of the furnace, absorb moisture, andmay be problematic to maintaining vacuum within the furnace. Glass wooland firebrick, other traditional insulating materials, are not robust tothermal shock, and expel moisture and particulates that contaminate thefurnace environment. Molybdenum sheets and other materials that functionas a thermal mirror need to be replaced frequency and require a longcooling cycle.

Using insulating sheets 136 with insulation cylinder 108 also lendssuperior thermal performance as compared to a traditional insulationpackage constructed of ceramics, molybdenum sheets, glass wool, and/orfirebrick. Graphite handles high temperatures well, is easy to machine,has a high resistivity, and is very efficient (e.g., approximately85-90% efficient). Thus, insulating sheets 136 improve the heating cycleof induction furnace 100 and are approximately 60% more energy efficientand 30% more time efficient as compared to a traditional insulation.

As a result of the enhanced insulating properties gained by theinclusion of insulating sheets 136, induction furnace 100 may beoperated to heat a workpiece at temperatures greater than the previouslimit of 1200 degrees Celsius without experiencing dielectric breakdownaround the coil 118 of induction furnace 100. For example, inductionfurnace 100 may be operated at temperatures above 1900 degrees Celsius.Also, insulating sheets 136 provide improved temperature control andreduced run-to-run variation. The improved insulation enables areduction in power consumption and reduced cycle time.

FIG. 1 illustrates induction heating system 102 in a raised or heatingposition where workpiece 122 is positioned within susceptor 120 and isready for heating according to induction furnace principles as describedabove. As shown in FIG. 2, induction heating system 102 is in a loweredposition where access to workpiece 122 through a door 160 of chamber 104is possible. Induction furnace 100 also includes a vacuum pump 162 forcreating a vacuum within the chamber 104. Door 160 forms a hermetic sealwhen closed such that a vacuum created by vacuum pump 162 in an interiorvolume of chamber 104 is hermetically isolated from an ambientenvironment outside chamber 104.

In operation of induction furnace 102, the workpiece 122 is in a raisedor heating position, i.e., within in a “heating zone” 164 defined bysusceptor 120, when a heating operation is being undertaken. Theworkpiece 122 is then moved to the lowered or cooling position, i.e.,within in a “cooling zone” 166 outside of the susceptor 120, when acooling operation is being undertaken. Moving workpiece 122 to thecooling zone 166 after completion of the heating of workpiece 122 allowsfor a reduction in the primary overall furnace cycle time. That is, thetime required for cooling workpiece 122 is an important factor in theoverall furnace cycle time, as traditional cooling becomes increasinglyinefficient at lower temperatures. According to embodiments theinvention, faster cooling times are achieved at lower temperatures bydropping the parts out of the hot zone 164 and into the cool zone 166 ofthe vacuum chamber 104.

According to an exemplary embodiment of the invention, induction furnace102 is constructed so as to facilitate movement of the workpiece 122between the heating zone 164 and the cooling zone 166 while maintaininga desired vacuum pressure within chamber 104, and is further constructedto include elements to enhance cooling of the workpiece 122. Referringnow to FIGS. 3 and 4, induction furnace 102 is shown as including acooling system 168 for cooling chamber 104 after the workpiece 122 hasbeen heated as desired. Cooling system 168 can include a heat exchanger170 and a blower 172. Hot gas within the chamber 104 is drawn into theheat exchanger 170, and cooler gas is blown back into chamber 104 byblower 172.

After completion of a heating of workpiece 122, the second cover 128 andtray 130 are dropped using a vacuum-sealed bellows system 174 attachedto second cover 116. Bellows system 174 includes a pair of vacuum-sealedbellows 176, 178 attached to respective coupling device 180, 182 thatare coupled to chamber 104. A linear actuator 184 such as a piston iscoupled to chamber 104 and is coupled to bellows 176, 178 via a plate186. Embodiments of the invention contemplate that linear actuator 184may be a pneumatic or hydraulic piston, an electro-mechanical piston, amanual actuator, or the like. The interior volumes of bellows 176, 178and coupling devices 180, 182 are fluidly coupled to the interior volumeof chamber 104. In this manner, movement of linear actuator 184 from theoutside of chamber 104 allows the atmosphere and pressure inside chamber104 to be maintained when plate 186 is moved either away from or towardchamber 104. Accordingly, workpiece 122 can be lowered from heating zone164 to cooling zone 166.

According to various embodiments, the movement to the cooling positionor zone may be governed by a threshold time and/or temperature, and maybe triggered by pressure or RGA or partial pressure, or rates of any ofthese. In one embodiment, the part or workpiece 122 is dropped into thecool section 166 after the part has cooled to approximately 1200° C.This effectively opens the insulated hot zone 164 and allows the coolinggas to pass across the heated parts 122. Once the workpiece 122 dropsout of the hot zone 164, the workpiece 122 experiences improvedradiative and convective cooling. The area of the cooling zone 166within chamber 104 has unique temperature control (i.e., ability toquench from high temperature to a lower, controlled temperature), whichis particularly useful for heat treating applications. Due to themulti-zone configuration of the vacuum chamber, cooling times may begreatly reduced when compared with cooling inside heating zone 164, andfaster cycle times can be met.

Referring now to FIG. 5, and with continued reference to the furnace ofFIGS. 3 and 4, a technique 188 for heating and cooling a workpiece isillustrated according to an embodiment of the invention. As illustratedin FIG. 5, certain steps in the technique 188 are considered to beoptional, as they would only be performed when the induction furnace isof a type as shown in FIGS. 3 and 4 or in certain workpieceheating/cooling processes. These optional steps in technique 188 areshown in phantom in FIG. 5, so as to highlight that they may not beperformed in induction furnaces having a certain geometry/construction.

As shown in FIG. 5, the technique begins at STEP 190 with loading of aworkpiece 122 into the furnace 100, such as by way of door 160, with thepiece being positioned on tray 130 when it is in a lowered position. Thefurnace door 160 is then closed, and the technique continues at STEP192, where the interior of the furnace 100 is brought to a high vacuum(when the induction furnace is configured as a vacuum inductionfurnace), such as a 10⁻⁷ vacuum pressure, by operation of vacuum pump162. The workpiece 122 is then raised into the upper hot zone chamber164 formed by insulating cylinder 108 and susceptor 120 at STEP 194. AtSTEP 196, the workpiece 122 is flushed with argon, and the interior ofthe furnace 100 may then be subsequently brought again to a high vacuumdepending on the furnace configuration. The workpiece then begins to beheated at STEP 198, with an inert gas (e.g., nitrogen) then beingintroduced at partial pressure at STEP 200. The workpiece 122 is heatedto 200-600° C. with the flowing inert gas to expedite removal ofoff-gassing, and the technique then continues at STEP 202 where thefurnace chamber may again be (optionally) returned to a high vacuum viavacuum pump 162 and heated to a desired processing temperature. Amaterial for coating the workpiece is then introduced if desired at STEP204.

The workpiece is begun to cool at STEP 206, with such cooling occurringinside the vacuum in certain embodiments. According to an embodiment ofthe invention, the workpiece is cooled to a temperature below a coolingthreshold, and the workpiece is lowered out of the heating zone 164 andinto the cooling zone 166 after the threshold has been met using thevacuum sealed bellows system 174 at STEP 208. In this manner, the vacuumpressure created inside the furnace may be maintained when moving theworkpiece to the cooling zone 166. A quenching gas such as helium,argon, or nitrogen is then injected at STEP 210, with the gas beinginjected at atmospheric pressure according to one embodiment.

According to various embodiments, gas may be injected at STEP 210 ateither or both of the high and low workpiece positions, as fastercooling times can be achieved at lower temperatures by dropping theworkpiece out of the hot zone 164 into the cool section 166 of thevacuum chamber 104. Thus, the process of injecting gas at STEP 210 canincorporate a repositioning of the workpiece down into the cooling zone166 outside of susceptor 120 by lowering hot zone tray 130. As set forthabove, the lowering of the workpiece 122 down into the cooling zone 166may be governed by a threshold time and/or temperature, and may betriggered by pressure or RGA or partial pressure, or rates of any ofthese. In one embodiment, the workpiece 122 is dropped into the coolsection after the workpiece has cooled to approximately 1200° C., asfurther cooling below this threshold temperature is achieved mostefficiently by passing cooling gas across the heated workpiece 122 whenit is located in the cooling zone 166. By selectively positioning theworkpiece 122 in the hot zone 164 and the cooling zone 166, the coolingtime of the workpiece can be reduced greatly and faster cycle times canbe met.

Referring now to FIG. 6, an induction furnace 220 is shown according toanother embodiment of the invention. While the induction furnace 220 isconstructed to have an insulating jacket assembly 110 identical to thatshown and described with respect to FIGS. 1-4 (with the insulatingsheets 136 arranged in layers to cover the exterior surfaces ofsusceptor 120), the induction furnace 220 shown in FIG. 6 is constructedas a furnace that does not operate at a vacuum, but instead providescooling to a workpiece 118 via a gasflow that has a non-recirculatedflow path. As shown in FIG. 6, gas blower 144 provides a supply ofcooling gas into the interior volume of the chamber 104 that is blownacross the workpiece 118. After the cooling gas is blown across theworkpiece 118, it is not recirculated through a cooling system forsubsequent use, but is instead vented from the chamber 104 of inductionfurnace 220 out through an exit port 222 and to the ambient environmentafter cooling of the workpiece is performed.

Therefore, according to one embodiment of the invention, an inductionfurnace for heating a workpiece includes a chamber, an insulationcylinder positioned within the chamber, and an induction coil positionedto surround at least a portion of the insulation cylinder. A susceptoris positioned within the insulation cylinder and inductively heated bythe induction coil when a current is provided to the induction coil. Aninsulating jacket assembly including one of a carbide material and arefractory metal is positioned in a space between the insulatingcylinder and the susceptor.

According to another embodiment of the invention, an induction furnaceincludes a chamber having a susceptor positioned therein. An interiorvolume of the susceptor defines a zone within the chamber for heating aworkpiece. The induction furnace also includes an insulation packagehaving a fused quartz cylinder positioned around the susceptor and agraphite jacket positioned between the fused quartz cylinder and thesusceptor. A coil surrounds the insulation package and is configured toinductively heat the interior volume of the susceptor when a current isprovided to the induction coil.

According to yet another embodiment of the invention, a method of makingan induction furnace includes providing a vacuum chamber, coupling aninsulation cylinder within the vacuum chamber, and coupling an inductioncoil to surround at least a portion of the insulation cylinder. Themethod also includes coupling a susceptor within the insulation cylinderand encapsulating the susceptor with an insulating jacket, wherein theinsulating jacket comprises one of a carbide material and a refractorymetal.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. An induction furnace for heating a workpiece, the induction furnace comprising: a chamber; an insulation cylinder positioned within the chamber; an induction coil positioned to surround at least a portion of the insulation cylinder; a susceptor positioned within the insulation cylinder, the susceptor being inductively heated by the induction coil when a current is provided to the induction coil; and an insulating jacket assembly comprising one of a carbide material and a refractory metal, the insulating jacket assembly positioned in a space between the insulating cylinder and the susceptor.
 2. The induction furnace of claim 1 wherein the insulating jacket assembly is sized to substantially surround the susceptor.
 3. The induction furnace of claim 1 wherein the insulating jacket assembly further comprises a plurality of layers.
 4. The induction furnace of claim 3 wherein a first portion of the plurality of insulating layers surrounds a side wall of the susceptor.
 5. The induction furnace of claim 3 wherein a second portion of the plurality of insulating layers is positioned above a top surface of the susceptor; and wherein a third portion of the plurality of insulating layers is positioned below a bottom surface of the susceptor.
 6. The induction furnace of claim 1 further comprising: a first graphite plate; and a second graphite plate; and wherein the first and second graphite plates are positioned to retain the insulating jacket assembly against the susceptor.
 7. The induction furnace of claim 1 wherein the insulating jacket assembly comprises a graphite felt.
 8. The induction furnace of claim 1 wherein the insulating jacket assembly comprises a material that is transparent to induction.
 9. The induction furnace of claim 1 further comprising a linear actuator coupled to the chamber and a bottom cover of the insulation cylinder; and wherein the linear actuator is configured to translate the bottom cover between a raised position, wherein the workpiece is positioned in a heating zone of the induction furnace within the susceptor, and a lowered position, wherein the workpiece is positioned in a cooling zone of the induction furnace, outside of the susceptor.
 10. The induction furnace of claim 9 further comprising a bellows system coupled to the bottom surface of the insulation cylinder; wherein the bellows system has an interior volume fluidly coupled to an interior volume of the chamber; and wherein the bellows system is configured to maintain a hermetic seal in the chamber from an ambient environment during movement of the bottom cover between the raised and lowered positions.
 11. An induction furnace comprising: a chamber having a susceptor positioned therein, wherein an interior volume of the susceptor defines a zone within the chamber for heating a workpiece; an insulation package comprising: a fused quartz cylinder positioned around the susceptor; and a graphite jacket positioned between the fused quartz cylinder and the susceptor; and a coil surrounding the insulation package and configured to inductively heat the interior volume of the susceptor when a current is provided to the induction coil.
 12. The induction furnace of claim 11 wherein the graphite jacket comprises a plurality of layers of graphite felt.
 13. The induction furnace of claim 11 wherein a first portion of the graphite jacket surrounds a side wall of the susceptor; wherein a second portion of the graphite jacket covers a top cover of the susceptor; and wherein a third portion of the graphite jacket covers a bottom cover of the susceptor.
 14. The induction furnace of claim 11 further comprising: a first graphite plate positioned between the fused quartz cylinder and a top surface of the susceptor; and a second graphite plate positioned between the fused quartz cylinder and a bottom surface of the susceptor.
 15. The induction furnace of claim 11 further comprising: a linear actuator coupled to a bottom cover of the fused quartz cylinder and configured to move the bottom cover in vertical manner between a raised position and a lowered position; and a vacuum-sealed bellows system configured to maintain a vacuum pressure in the chamber during movement of the bottom cover of the fused quartz cylinder between the raised position and the lowered position by way of the linear actuator.
 16. A method of making an induction furnace comprising: providing a vacuum chamber; coupling an insulation cylinder within the vacuum chamber; coupling an induction coil to surround at least a portion of the insulation cylinder; coupling a susceptor within the insulation cylinder; and encapsulating the susceptor with an insulating jacket, wherein the insulating jacket comprises one of a carbide material and a refractory metal.
 17. The method of claim 16 further comprising positioning a pair of graphite plates at respective top and bottom exterior surfaces of the susceptor.
 18. The method of claim 16 wherein encapsulating the susceptor with an insulating jacket comprises covering exterior surfaces of the susceptor with a plurality of layers of graphite felt.
 19. The method of claim 16 further comprising: encapsulating a side wall of the susceptor with a first portion of the insulating jacket; encapsulating a top surface of the susceptor with a second portion of the insulating jacket; and encapsulating a bottom surface of the susceptor with a third portion of the insulating jacket.
 20. The method of claim 16 further comprising: coupling a bellows system to a bottom surface of the insulation cylinder, the bellows system having an interior volume fluidly coupled to an interior volume of the chamber; coupling a linear actuator to the bellows system; and configuring the linear actuator to selectively translate the bottom cover of the insulation cylinder between open and closed positions. 